Dear Richard, Very nice to hear from you, and thank you a lot for the help! Indeed, I have cleaned the erosion still not working.
I am trying to now* remeasure the break voltage of the diode*. I suspect that the doping get diffused in the isolation layer after age, which make it a good diode, but with different parameter for the step recovery. >From what I see in the circuit, I understand that *I need to tune the * *resonance at a given frequency to have higher voltage to make sure * *the diode reversely discharged*. I noted the tuning is very tricky, as the waveguide assembly is also a part of the resonance circuit. *Do you have a internal dimension of the assembly*, that will help speed up with the EM calculation to understand which screw for what. Best regards, Kj 2017-12-25 2:42 GMT+08:00 Richard (Rick) Karlquist <rich...@karlquist.com>: > I extensively studied the 5061 harmonic generator when I > was designing the harmonic generator in the 5071A. > We are now going on 30 years since that work. The diode > had some HP part number. Even if you knew this part > number, you would need to have the Part Information Report > microfiche that gave the vendor part number. The > chances of this diode still being available are very slim. > So you are not going to get an exact replacement, except > by cannibalizing another 5061 harmonic generator assembly, > assuming it doesn't also have a bad diode. As far as > replacing it with a different diode, that too would be > questionable. SRD's have magic unspecified parameters > when it comes to what they do in a circuit. The 5061 > generator in particular has extremely high efficiency > due to its unique design. It was designed by a Korean > professor named Soon Choi (IIRC) who spent a summer > at HP. He left no known documentation as to how the > design works, or how to specify the SRD. > > After a long period of study, I concluded that I was > never going to match the efficiency in any simple > circuit. The diode mounted directly in the waveguide > is the magic. Fortunately, by that time, we could use > a phase locked DRO and get around this problem. Len > Cutler in his usual style criticized me for "taking the > easy way out", but he eventually came around to my > way of thinking. > > I will give you a little hope. The harmonic generator > consists of a bunch of silver plated parts that are > supposed to fit together and achieve electrical conductivity. > After many years, the silver and tarnish and upset the > electrical conductivity. You might try disassembling > the diode mount and cleaning up everything. After > you reassemble it, you might have good news. > > I will say that I have never heard of an SRD failing, > and as you say, it looks good at DC. What possible > failure mechanism could selectively make the diode > stop generating harmonics but other wise be OK at DC? > Somehow let the pixie dust escape without letting the > smoke escape. Seems unlikely. > > Also check the drive circuitry. SRD's need tricky components > to make them "step" correctly. Again, poor grounding due > to corrosion could spoil the harmonic generation. > > Rick Karlquist N6RK > Member of the 5071A design team > > > On 12/24/2017 3:54 AM, Kejia Lee wrote: > >> Dear All, >> >> Happy Christmas! >> >> May I know if anyone knows the part number or the specification of the >> step >> recovery diode in the harmonic >> generator for the old HP 5601A cesium frequency standard? >> >> I recently received this toy. The cesium tube seems to be OK, and I had >> located the problem being >> no 9GHz from the waveguide. I checked the diode, the DC properties seems >> to >> be OK, but just >> can not generate frequency comb any more. I really hope I can repair it as >> a personal new-year gift. >> >> I will be really appreciated, if you had any suggestions. >> >> Best regards, >> >> K. >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/m >> ailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.